1. Field of the Invention
The invention relates to a device for locking the steering column of a vehicle as needed, comprising a force-loaded locking member, and comprising a control device which adjusts the locking member relative to the steering column between two positions, that is, a locking position in which the rotation of the steering column is prevented and a release position in which a rotation is possible.
2. Description of the Related Art
In the known device of this kind the locking member is comprised of a profiled bolt which in the locking position of the device is introduced by a motor into a crown gear (DE 199 24 835 A1) or into a hollow profiled section (DE 199 29 435 A1) of the steering column.
In the aforementioned device the bolt is movable together with a lifting member driven by a motor, and an interposed spring loads the bolt in the ejection direction. Moreover, a restoring force constantly acts on the lifting member and attempts to push the bolt against the hollow profiled section of the steering column. In the locking position the bolt can engage the steering column only in certain rotational positions while locking is not possible in the other rotational positions. On the other hand, upon movement into the release position the removal of the bolt from the hollow profiled section can be difficult. This happens, for example, when the steering column, while in the locked position, has been rotated by the amount of play that is available and this rotation is fixed because the wheels of the vehicle are pushed against the curb.
It is an object of the present invention to develop a simple, reliable device of the aforementioned kind with which the aforementioned disadvantages can be prevented.
In accordance with the present invention, this is achieved in that the locking member is comprised of at least one clamping jaw which has a substantially smooth friction surface without surface profile (pattern), in that on the circumference of the steering column a substantially smooth counter friction surface without surface profile (pattern) is provided, and in that the control device acts on a force generator which in the locking situation exerts a clamping force onto the clamping jaw directed against the counter friction surface, but turns off this clamping force in the release position.
The invention thus avoids a positive-locking engagement between the locking member and the steering column and provides instead a frictional locking position between the friction surface of a clamping jaw and a counter friction surface of the steering column. In this way, immediately in any of the rotational positions of the steering column, a reliable locking position is possible, and, moreover, the movement into the release position is possible always without disturbances. This is made possible by a force generator which exerts a clamping force onto the clamping jaw in the locking position and thus forces its friction surface against the counter friction surface of the steering column. In the release position, on the other hand, the clamping force is switched off and the friction surface is released relative to the counter friction surface. A minimal travel is sufficient between the locking position and the release position of the clamping jaw. The air gap must be only tenths or hundredths of a millimeter in the release position.
A clamping jaw can surround half the circumferential area of the steering column. This areal contact provides a high clamping force load and results in an excellent steering column guiding action. This can be improved when the oppositely positioned circumferential area of the steering column is covered by a mirror-symmetrically arranged additional clamping jaw. In this way, the device, in particular, when it is configured as a mirror-symmetrical clamping jaw pair, can take over the function of a rotational bearing for the steering column. In this way, it is possible with the invention to eliminate an otherwise required bearing for the steering column.
For increasing the clamping force, the clamping jaw or the clamping jaws can be comprised of several segments which are movable segment by segment radially toward the steering column axis. Wedge profiles on the counter segments and, optionally, counter wedge profiles provided on the moveable control members generating the clamping force can generate a set of clamping forces acting segment-by-segment which are oriented toward one another in a radially staggered arrangement. Such a control member can be comprised of a clamping ring which in the locking situation engages the locking members and effects the required radial pressing action of the individual segments.
Because a positive-locking engagement is avoided, the movement between the locking position and the release position, and vice versa, occurs completely silently. Because of the minimal adjustment stroke of the clamping jaw or the clamping jaws or its/their segments and because of the clamping force or release force being generated only as needed, small-size drives are sufficient which are not only inexpensive but also space-saving. This is so particularly because of the wedge drives for generating the clamping force or the release force to be described in the following.
In particular, when a clamping jaw pair is configured as a constructive unit in the form of a clamp surrounding the steering column and secured against rotation, there is also a theft protection provided for the vehicle furnished with this device. Removing the clamping sleeve from the device housing has no effect in the locking situation because the clamp loaded by the clamping force prevents a rotation of the steering column even in the demounted state of the clamping sleeve. Accordingly, in the device according to the invention no special provisions are required in order to make the access to the clamping jaw or the clamp difficult or to prevent its demounting. Eliminating such safety measures saves space as well as manufacturing and assembly costs.